To overcome such problems, the use is known of obstacle detection systems able to make the above manoeuvres easier and, more specifically, able to exactly determine the distance between the vehicle and the obstacles located along its path.
The detection systems comprise sensor means, generally consisting in a series of active sensors of the ultrasonic type, in which each sensor features piezoelectric capsules able to transmit a sound signal consisting in a series of pulses (bursts) transmitted inside a preset range of action.
Any obstacles inside the range of action create a reflected echo signal which is then received by the piezoelectric capsules.
The echo signal received this way and which falls within a specific time window, is compared with a threshold signal correlated at the minimum distance allowed between the vehicle and an obstacle; in the event of this threshold signal being exceeded by the received echo signal, the sensor sends a warning signal to a control unit which converts it into a signal that can be heard by the driver.
It is of crucial importance to eliminate or restrict the possibility of wrong signals to the driver due to the detection of objects that are too far away or to the detection of special conformations and protrusions of the car, such as, for example, a towing hook fastened behind the vehicle, special types of bumper bars or spoilers, spare tyres secured behind off-road vehicles, etc.
For this purpose, sensor regulation is known at the time of installation so as to exclude any vehicle protrusions from their range of action.
Also known is the definition of the time window in which the received echo signal is considered useful for comparison with the threshold signal, so as to exclude the detection of objects that are too far away or too close.
These known detection systems are not however without drawbacks, among which the fact that any modifications to the vehicle following sensor installation, such as the fitting of a tow hook, requires new calibration of the system by direct intervention on the sensors.
Moreover, a reduction in the extension of the useful time window, so as to exclude the echo signal due, for example, to the tow hook, considerably restricts the range of action of the sensors, with the risk of the vehicle knocking against obstacles not detected by the system.